Register: Counter A and Counter B Control Registers.

((PUB ┆ PRI))
  CTRA

((PUB ┆ PRI))
  CTRB

Returns: Current value of Counter A or Counter B Control Register, if used as a source variable.

Explanation

CTRA and CTRB are two of six registers (CTRA, CTRB, FRQA, FRQB, PHSA, and PHSB) that affect the behavior of a cog's Counter Modules. Each cog has two identical counter modules (A and B) that can perform many repetitive tasks. The CTRA and CTRB registers contain the configuration settings of the Counter A and Counter B Modules, respectively.

The following discussion uses CTRx, FRQx and PHSx to refer to both the A and B pairs of each register.

Each of the two counter modules can control or monitor up to two I/O pins and perform conditional 32-bit accumulation of the value in the FRQx register into the PHSx register on every clock cycle. Each Counter Module has its own phase-locked loop (PLLx) which can be used to synthesize frequencies from 64 MHz to 128 MHz.

With just a little configuration and in some cases a little maintenance from the cog, the counter modules can be used for:

• Frequency synthesis
• Frequency measurement
• Pulse counting
• Pulse measurement
• Multi-pin state measurement
• Pulse-width modulation (PWM)
• Duty-cycle measurement
• Digital-to-analog conversion (DAC)
• Analog-to-digital conversion (ADC)
• And more.

For some of these operations the cog can set the counter's configuration, via CTRA or CTRB, and it will perform its task completely independently. For others, the cog may use WAITCNT to time-align the counter's reads and writes within a loop; creating the effect of a more complex state machine. Since the counter's update period may be brief (12.5 ns at 80 MHz), very dynamic signal generation and measurement is possible.